Combustors, such as those used in industrial gas turbines, for example, mix compressed air with fuel and expel high temperature, high pressure gas downstream. The energy stored in the gas is then converted to work as the high temperature, high pressure gas expands in a turbine, for example, thereby turning a shaft to drive attached devices, such as an electric generator to generate electricity.
As the air/fuel mixture combusts, the hot gas that is generated creates fluctuations in pressure. These pressure fluctuations at certain frequencies (e.g., 1-1000 Hz) create acoustic pressures through the system. Acoustic pressure fluctuations in the combustion system can cause serious damage to the hardware if they excite the natural frequency of a component. Exciting the natural frequency of a component causes oscillation of that component in the system, thereby weakening, if not, destabilizing the structural integrity of the system.
There are known ways of preventing the excitation of natural frequency within the system. Acoustic pressure fluctuations that can generate natural frequencies may be reduced by redesigning the hardware, changing air splits, or adding resonators to the system. However, in large applications such as an industrial gas turbine, for example, this can result in adding significant cost or reduction of the combustion system performance as extensive time for tests and modifications are needed. Additionally, external resonators for this purpose can reduce the combustor performance as the resonator will need air for damping. The air will be taken away from combustion, thereby decreasing the efficiency of the combustion. Such may result in increased emission levels, metal temperature, and thermal stresses, all of which will affect the life and performance of the structure of the system.